1. Field of the Invention
This invention relates to well tools and more particularly to seal elements for use on dual well packers.
2. Related Art and Information
Multiply completed wells are so constructed as to permit simultaneous and separate production from two or more different pay zones. Early dual wells were provided with a single string of tubing and had a single well packer between the two pay zones. The lower zone produced through the tubing and the upper zone produced through the tubing-casing annulus.
Multiple completions were later improved to make them easier to control, safer, and more economical. For many years it has been common practice to provide a string of tubing for each of the multiple pay zones with a multiple packer above each pay zone except for the lowermost zone which has a single packer above it. Thus, such a well has a single packer between the lower two zones, a dual packer above the next upper zone, a triple packer above the next, and so on. Thus, a dual packer has two mandrels passing through its seal elements, a triple packer has three, and a quadruple packer has four.
In addition to mandrels passing through the seal elements, it is often desirable to also have other elongate cylindrical members extend through the elements. Such cylindrical elements may include control lines, bypass tubes, injection tubes, as for chemicals for instance, electrical lines, electrical feed through connections, or the like.
In many cases, the seal elements of multiple packers have successfully held only moderate pressures without leaking. It has been desirable to provide seals which would hold much higher pressures without leaking.
Applicant is familiar with the following listed prior patents which disclose dual packers, each being hydraulically actuated and each having a central seal element disposed between upper and lower end elements.
______________________________________ 3,167,127 3,288,218 3,381,752 3,851,705 4,413,677 4,505,332 4,512,399 4,852,649 ______________________________________
U.S. Pat. No. 3,167,127 which issued to Phillip S. Sizer on Jan. 26, 1965; U.S. Pat. No. 3,288,218 which issued to Carter Young on Nov. 29, 1966; U.S. Pat. No. 3,381,752 which issued to Thomas L. Elliston on May 7, 1968; U.S. Pat. No. 3,851,705 which issued to Marion Barney Jett, et al, on Dec. 3, 1974; U.S. Pat. No. 4,413,677 which issued to Donald H. Perkins on Nov. 8, 1983; U.S. Pat. No. 4,505,332 which issued to Aubrey C. Mills, et al, on Mar. 19, 1985; and U.S. Pat. No. 4,512,399 to John C. Gano and Donald H. Perkins on Apr. 23, 1985, each show a hydraulically actuated dual packer on which is mounted a set of packer seals. This seal set consists of three elements: a central dual element between an upper and a lower end element. These seal sets are obviously well known and have been in use for years, and are of a type which has been known to leak at much lower pressure than has seemed reasonable.
U.S. Pat. No. 4,852,649 issued to Carter R. Young on Aug. 1, 1989 and discloses packer elements for multiple well dual packers. These packer elements are molded in one or two pieces. Each of these elements is formed with slots, slits, or slip surfaces for allowing one portion of the polymeric body of the element to move or slip relative to an adjacent portion thereof in order to provide more uniform distribution of stresses within the elements when they are compressed longitudinally to cause them to expand laterally to sealing engagement between the dual mandrels of the packer and the inner wall of the well casing. While such elements brought about more uniform distribution of stresses in the elements, the problem was not solved because the polymeric material of the element body had to move too far in certain areas, and this resulted in frequent failure due to leakage.
The present invention is an improvement in dual packer elements, and in particular an improvement over the dual packer elements disclosed in U.S. Pat. No. 4,852,649 to Carter R. Young. The present invention provides multiple packer elements which function more efficiently to seal against both low and high differential pressures, provide good distribution of stresses in the polymeric material of the elements, and greatly minimizes the maximum distance which any portion of the element is required to travel and the associated elastic strain in its deformation from its relaxed condition to its expanded sealing condition. Further, these improved dual elements lend themselves more readily to the molding processes and can, thus, be manufactured with greater facility and more economically.